units

Protel
Protel is yet another company that makes COCOT phone equipment. They have about 4 models of pay phones in widespread use. Most of these phone models are very similar with only slight differences between them. They are all line powered. When dialing a call on a Protel phone, the phone slowly dials each digit while it waits for you to finish dialing or finish paying. You may able to hear this in the background, but it is really quiet. These phones take your money at the end of the call. They will all just tell you to deposit more money if you haven't paid enough. And if you leave them off the hook too long, they produce an interesting beeping sound. Some of these phones have credit card slots which accept many major credit cards. Most of these models have the extended *#6X series of interesting secret codes. *#61 is the code to hear the phone say its number. *#62 is the code to hear the software version and model numbers. *#65 sometimes discloses the phone company's modem number. The phone company can program the phone to prevent you from using these codes. Where the Protel phone models differ is in their phone voices, internal phone modems and ringers as well.

Model 2000
This is the oldest model. It uses the old phone voice and has a 300 baud only modem. The phone voice on this model seems to have more background noises and hums than other models. This modem seems extra sensitive to certain tones, so I recorded some calls to this type of phone. The first one is just a call where I don't make any noise. The second one is where I play certain tones that make the modem come back on again and again. The model 2000 is the only phone without extended *#6 codes, so you are just stuck listening to the date and time of the last modem call to or from the phone company. When dialing a number on this phone, the touch tones seem to have a sort of grinding sound in them. Other Protel phones do not have this. A recording of the ringer from a Protel 2000 is now available.

Model 4000
This is the middle age model. Some of them have the old phone voice, while others have the new phone voice. The modem supports 300 and 1200 baud, but it is extra sensitive to any noise at 300 baud. I have recorded 2 calls to this phone. In the first one, I remain silent. In the second one, I belch at the pay phone, and it tries to connect to me at 300 baud. A recording of the ringer from a Protel 4000 is now available.* This model of phone can run on a coin line. Coin line usage of this model is done by local phone companies such as Qwest, Verizon and Telus (in Canada) for their normal pay phone service. Sprint has also used this model of phone for normal pay phone service, but they don't use coin lines, so it acts more like a COCOT.

Model 7000
This is Protel's newest model of pay phone. It uses only the new phone voice, and it has the world's weirdest modem. It uses some nonstandard mode of 1200 baud so you can't call it with your normal modem. This model also supports coin line use. I have also recently noticed that if I call two of these phones at the same time, and have a conference call between them, the modems will try to connect to each other. I have recorded that for your listening pleasure as well as a normal call to one of these phones. Also I have recorded the ringer.
Normal Call
2 Protel 7000s trying to connect to each other
Ringer

Model 8000
This is awfully similar to the model 4000. It has the same modem in it, and it uses either the old phone voice, the new phone voice, or the 2002 phone voice, which I have only heard at one phone and haven't recorded yet. This phone is designed to fit inside a Western Electric pay phone housing so it can be used by Regional Bell Operating companies. One company that I have seen use this phone is Qwest, they have used it both on a coin line as a normal pay phone, and on a normal phone line as a true COCOT. Qwest's usage of this kind of phone is rather limited when compared to BellSouth. During my recent travels to BellSouth territory, this was the only kind of phone BellSouth ever used. They are run on normal phone lines, not coin lines, regardless of whether BellSouth is the LEC in an area or not.

Other protels Protel also has some newer models with digital displays and card slots. Their basic card/display model, which was aimed at international markets, has an LCD display and six multipurpose buttons, which could be programmed as speed-dials or as language select buttons. Protel recently discontinued this model, which didn't have a name. Their other advanced model is called the Ascension. It looks an awful lot like a Nortel Millennium phone, but it has a coin return button, and the coin slot is on the right. These models use the same 7000 model circuitry as standard COCOTs, so I don't need to describe anything special about their operation.  

with thanks to  http://www.payphone-directory.org/phones.html